Computer storage devices, such as disk drives, use read/write heads to store and retrieve data. A write head stores data by utilizing magnetic flux to set the magnetic moment of a particular area on a magnetic media. The state of the magnetic moment is later read by a read head which senses the magnetic fields.
Conventional thin film read heads employ magnetoresistive material, generally formed in a layered structure of magnetoresistive and non-magnetoresistive materials, to detect the magnetic moments of the data bits on the media. The data bits are positioned in concentric tracks on the storage media. Decreasing the width of these tracks allows an increase in the storage capacity of the media (more tracks per inch). However, the width of the tracks are limited by how narrow both the read and write reads can be made.
The width of conventional read heads have been limited by their method of fabrication. One such method is shown in FIGS. 1a-e. 
The first step of this process is shown in FIG. 1a and involves depositing a sensor material 20 on top of a layer of alumina 10. The senor material is typically a multi-layered anisotopic magneto-resistive (AMR) or spin valve material.
Next, as shown in FIG. 1b, a bi-layer photoresist layer 30 is applied directly on top of the sensor material 20. The bi-layer photoresist 30 has a soft base layer 32 and a hardened overhanging image layer 34. The bi-layer photoresist 30 is positioned directly above the desired position of the sensor element 22 (not shown). As will be further explained, the width of the sensor 22, and thus of the readable track, is limited by the height hb of the base layer 32 of the photoresist 30.
FIG. 1c shows the next step of etching the sensor material 20. During this step sensor material 20 on either side of the sensor element 22 is etched away by an ion beam etch. As can be seen, the ion beam etch removes the sensor material 20 which is not under or immediately adjacent the bi-layer photoresist 30. During this step the shadow of the overhang 36 of the image layer 34 of the photoresist is used with the ion beam set at an angle to define the sensor element 22 with slanted sides 24. Some of the etched sensor material 20xe2x80x2 will deposit itself over the photoresist 30.
In the next step, a hard bias 40 and lead material 50 are deposited. This is shown in FIG. 1d. The hard bias 40 is deposited over the alumina 10 arid the sides 24 of the sensor 22 up to near the base layer 32 of the photoresist 30. After the hard bias 40 is deposited, the lead material 50 is deposited over the hard bias 40 and up against the side walls 33 of the base layer 32.
The last step of this process is shown in FIG. 1e. During this step the bi-layer photoresist 30 is lifted off (removed) from the top of the sensor element 22. The resulting structure is a read sensor which has the sensor element 22 biased by the hard bias 40 and which a sensing current can be passed through the sensor element 22 by way of the leads 50.
One problem with this existing method of fabrication is that due to a geometric limitation inherent in a bi-layer overhang structure, the width of the sensor cannot be made less than a certain minimum amount. This limitation in turn limits the minimum width of the data track used. Specifically, the problem is that the bi-layer photoresist must be kept above a certain minimum to avoid fencing which can cause shorting. Fencing is a build-up of material ejected during the etch of the sensor material 20 along the side walls 33 of the photoresist 30. When fencing occurs the later removal of the photoresist will leave a spike of ejected material. This spike of material can contact other elements of the device and cause shorting.
Fencing can be avoided by maintaining an aspect ratio (the width wo of the overhang 36 relative to the height hb of the base layer 32) of at least 2. This allows the ejected material sufficient room to collect under the overhang 36 and not on the sides 33 which would cause fencing. Another geometric limitation is due to the thickness hb of the base layer 32. The base layer 32 must be thick enough to avoid the ejected material 20xe2x80x2 and the later deposited material 40xe2x80x2 and 50xe2x80x2, which collect on the photoresist 30, from extending far enough from the photoresist 30 to come in contact with the sensor 22. Clearly, with a bridge of material between the photoresist and the sensor, the hard bias 40 and lead material 50 will be improperly deposited. As such, to avoid such material bridging, it has been found that the base layer 32 must be thicker than a minimum of about 0.1 xcexcm.
Therefore, because of the necessary minimum thickness of the base layer hb (about 0.1 xcexcm) and the required minimum aspect ratio of the overhang 36 (about twice the thickness of the base layer, w0 about 0.2 xcexcm), the photoresist 30 typically cannot be narrower then about 0.5-0.6 xcexcm. Thus, the minimum track widths of the media used with read sensors made by this conventional method are limited to a minimum of about 0.5-0.6 xcexcm.
Additional problems with the conventional method include low film density and poor composition control of the multi-element materials deposited to create the read head. With the existing method, the hard bias material is sputter deposited over the sensor 22. The shadowing effect of the overhang 36 causes an uneven composition as the lighter mass element, such as cobalt, which can be deposited at higher angles (relative to the vertical), will be deposited in greater amounts under the overhang 36. The area under the overhang 36 will likewise have lesser amounts of the heavier elements such as platinum and tantalum. As a result, near the sensor junction there will exist low film density and varied material composition. Which in turn results in poor magnetic properties (e.g. Hc, and MrT) of the hard bias layer.
Therefore, a method is sought which will allow fabrication of apparatuses with significantly narrower read sensors, such that an increase in data storage can be achieved through the use of narrower data tracks. The method must fabricate the sensor in a manner which will avoid fencing and which will not result in low film density and poor composition control. Also, the method must perform these tasks while minimizing the cost and time of fabrication.
The method of the present invention is embodied in a method for fabricating a magnetoresistive head structure with a narrow read sensor.
In at least one embodiment of the method, the steps include obtaining a lead and magnetic bias layer, applying a photoresist layer over the lead and magnetic bias layer and about a desired position of a sensor (such that the desired position of the sensor is substantially free of the photoresist layer), etching the lead and magnetic bias material substantially at the desired position of the sensor, depositing a sensor at the desired position of the sensor, and removing the photoresist.
The step of obtaining a lead and magnetic bias layer can include depositing a lead layer and depositing a magnetic bias layer over the lead layer. It is preferred that the lead layer is deposited as a layering which includes a first tantalum layer about 50 xc3x85 thick, a gold layer about 300 xc3x85 thick positioned over the first tantalum layer, and a second tantalum layer about 50 xc3x85 thick positioned over the gold layer. The magnetic bias layer can be a hard bias layer or an exchange layer. It is preferred that the hard bias layer is deposited as a layering which includes an underlayer of chromium about 50-200 xc3x85 thick and a permanent magnet layer over the underlayer of cobalt chromium and platinum about 500 xc3x85 thick.
With the magnetic bias layer being an exchange layer, the method further includes a step of annealing to set the exchange. This step occurs after the step of obtaining the lead and magnetic bias layers. It is preferred that the annealing step is a magnetic anneal at about 400 C. It is also preferred that the exchange layer is deposited as a layering which includes a first nickel iron layer about 75 xc3x85 thick, a manganese nickel layer about 300 xc3x85 thick positioned over the first nickel iron layer, and a second nickel iron layer about 50 xc3x85 thick positioned over the manganese nickel layer.
The etching of the lead and magnetic bias material can be performed by an ion beam etch. During the etching, the lead and magnetic bias material can be etched to produce sloping sides adjacent to the desired position of the sensor. The sensor can be a magnetoresistive element. It is preferred that the sensor is either an anisotopic magnetoresistive element or a spin valve element. Further, it is preferred that the sensor has a sensing layer which is less than 0.6 xcexcm wide.
The photoresist layer used in the method is preferably a bi-layer photoresist having a base layer and an image layer over the base layer. The image layer overhangs the base layer at the points adjacent to the desired position of the sensor.
The apparatus of the invention is embodied in a magnetoresistive head structure. In at least one embodiment the magnetoresistive head structure has a sensor with sides, a lead layer with a portion positioned on either side of the sensor (the lead layer being in contact with the sensor so that a sensing current can flow between the portions and through the sensor), and a magnetic bias layer positioned over the lead layer and on either side of the sensor.
It is preferred that the lead layer includes a first tantalum about 50 xc3x85 thick, a gold layer about 300 xc3x85 thick positioned over the first tantalum layer, and a second tantalum layer about 50 xc3x85 thick positioned over the gold layer.
The magnetic bias layer can include either a hard bias layer or an exchange layer. The hard bias layer preferably includes an underlayer of chromium about 50-200 xc3x85 thick, and a permanent magnet layer over the underlayer of cobalt chromium platinum about 500 xc3x85 thick. In a preferred embodiment, the exchange layer includes a first nickel iron layer about 75 xc3x85 thick, a manganese nickel layer about 300 xc3x85 thick positioned over the first nickel iron layer, and a second nickel iron layer about 50 xc3x85 thick positioned over the manganese nickel layer.
The sensor can be a magnetoresistive element, preferably either an anisotopic magnetoresistive element or a spin valve element. Further, it is preferred that the sensor includes a sensing layer which is less than 0.6 xcexcm wide.